The present invention relates to an image reproducing apparatus which selectively superimposes a sub-video signal on a main video signal to produce a combined image.
FIG. 1 shows a configuration of an example of an image reproducing apparatus of the above kind. In FIG. 1, a main video signal source 1, for instance, a VTR (video tape recorder), outputs a main video signal representing a video image such as a usual moving picture. A sub-video signal source 2, for instance, a VDR (video disc recorder), outputs a sub-video signal representing characters or a graphic image. The main video signal from the main video signal source 1 is provided to a video monitor 4 such as a CRT display via a switch 3. The sub-video signal from the sub-video signal source 2 is provided not only to the switch 3 but to a comparator 5. As shown in part (a) of FIG. 2, the comparator 5 compares the level of the sub-video signal SUB VIDEO with a first predetermined value REF1. In the sub-video signal SUB VIDEO, portions to be superimposed that represent characters etc. are given white or other colors a little darker than white while the remaining portions are given black or dark colors. Therefore, the portions to be superimposed have a higher signal level. The comparator 5 outputs a first changeover signal CHANGE while the level of the sub-video signal SUB VIDEO is larger than the first predetermined value REF1. In response to the first changeover signal CHANGE, the switch 3 provides the sub-video signal, instead of the main video signal, to the video monitor 4. Thus, the video monitor 4 displays a combined video image in which, for instance, characters are superimposed on a moving picture.
In this type of conventional image reproducing apparatus, however, it may be the case that the sub-video signal from the sub-video signal source 2 includes a high-level pulse such as noise (shown by symbol A in FIG. 2). In such a case, if a mixed pulse has an amplitude larger than the predetermined value REF1, it is provided to the video monitor 4 with the switch 3 being changed over during that portion. That is, noise is mixed into the main video signal in its picture section that actually appears on the video monitor 4, which will impair the quality of a combined image.